Exhaust gas from diesel engines includes a variety of harmful materials, among which nitrogen oxide emissions and particulate matter have become more severely regulated by law.
In response to the more severe regulations, a diesel exhaust filter system has been developed, which consists of a diesel oxidation catalyst (DOC) for converting hydrocarbons and carbon monoxide of diesel exhaust gas into water and carbon dioxide through catalytic oxidation, and a diesel particulate filter (DPF) for trapping particulate matter emissions from diesel exhaust gas and burning them with the heat of the exhaust gas.
Recently, a mandatory diesel engine exhaust emission requirement has became more strict (from the Euro 3 standard to the Euro 4 standard), reducing the emission allowance for nitrogen oxide and particulate matter to a half of the previous one.
In addition, this newly established Euro 4 includes an emission standard which imposes requirements on emissions from diesel vehicles which have run a distance of 100,000 km. Accordingly, new diesel vehicles, if intended to be sold, must be manufactured to meet the pertinent items of the new regulation.
As a consequence of the more severe regulation, a catalyzed diesel particulate matter filter system consisting of a diesel oxidation catalyst (DOC) and catalyzed particulate filter (CPF) is newly mounted in diesel engine vehicles.
However, when the filter of the catalyzed diesel particulate filter system is renewed, the diesel oxidation catalyst is apt to be inactivated by the heat generated upon the exothermic reaction thereon with the hydrocarbons and carbon monoxide of the exhaust gas. In this regard, the exhaust gas is measured to have a temperature from 600 to 650° C. at the outlet of the catalyst bed while ranging in temperature from 400 to 450° C., so that the exothermic reaction on the catalyst is analyzed to increase the temperature from 150 to 250° C.
Moreover, as for a catalyst-coated filter, it has carbonaceous particulate matter accumulated therein, which is combusted by the exhaust gas, having a temperature of 600° C. or higher. The combustion of the carbonaceous particulate matter increases the temperature of the filter to 800° C., often 1000° C. or higher, thereby deactivating the catalyst.
Hence, in order to mount catalyzed diesel particulate filter systems in vehicles which are manufactured to meet the new standards, a performance test must be conducted to determine whether the catalyzed diesel particulate filter systems maintain their catalytic activity even after running 100,000 km (about 100 hours). This 100,000 km durability test is a factor increasing the time and cost needed to develop catalyzed diesel particulate filter systems.